I love subs - they are awe-inspiring, amazing feats of engineering and terrifying weapons.

I highly recommend watching various documentaries on them. I think I have consumed every sub dock I could find online.

https://www.youtube.com/watch?v=wHIS1I9tv78 is a great one. Also, note that the engineering needed to make the Global Explorer was new and significant. I think that with the making of that ship, the CIA gained a lot of know-how for sea-ops, which likely played at least a minor factor into their ability to make requirements/requests into the design of the Jimmy Carter sub, which is largely believed to be the sub they use to splice undersea cables/or cut them...

https://en.wikipedia.org/wiki/Project_Azorian

The sad thing about the end of the cold war is that the governments are spending less resources on establishing such hidden underground societies